You can do it! I've leveled up Inna and working on Silan and his quest, as it unlocks another character. They're all so different, very different play styles. I'm hooked lol
Slay the Spire is real shite in comparison. Like, this is next level card game.
I've spent, maybe $5 in total, because I wanted to pay something; it's such a huge game with massive variety, and with the quests and the forge and market bonuses you can get there is a sense of progression and purpose to the experience.
I think the key to completing quests is to really lean into the character card design. Some work extremely well with evasion cards, or arcane. Shock synergises the best with Inna. Burn synergises the best with Raodan. Arcane with Silan. But then branching out and experimenting with other status/debuffs adds another level to the gameplay.